A Mach-Zehnder interferometer (MZI) is a device for determining the relative phase difference between two collimated beams from a coherent light source. The interferometer is used to measure small phase difference in one of the two beams caused by a small sample or the change in length of one of the paths.
A MZI usually contains two cascaded fiber components that function as a beam splitter and combiner. The temperature sensitivity of this device is typically small because the thermo coefficient of silica fiber is small.
Another type of MZI based on dual core photonic crystal fiber (PCF) has been developed. This kind of MZI requires a special design of the fiber for selective infiltration and therefore has difficulties for a broad application.